Social media sites are driving children to commit violence and murders “within minutes”, Britain’s most senior police officer has warned.

Cressida Dick, the Metropolitan Police commissioner, said that often- trivial disputes between young people were escalating into murder and stabbings at unprecedented rates. The goading of rivals on online message boards and video sites “revs people up” and normalised violence, she said.

The speed at which disputes gathered pace echoed the way in which some Islamists, including the perpetrator of the lorry attack in Nice in 2016, were radicalised within days or weeks.

A febrile online atmosphere was among factors responsible for rising knife crime. Also to blame were drug-dealing, absent fathers and socio- economics, Ms Dick said.